1. Field of the Invention
The present invention relates generally to fabric inspection systems and, more particularly, to an apparatus for inspecting a tubular knitted fabric web at high speed without operator intervention.
2. Description of the Prior Art
In the manufacture of apparel, particularly T-shirts and the like, after the greige goods have been knit they are inspected and transferred to a finishing line. Inspection is usually accomplished by passing the fabric web in front of a light box. The light from the light box enables an operator to detect a hole or other defect in the fabric. The operator then stops the line, repairs the defect and restarts the line. If the operator misses a defect, the defect may catch inside machinery during subsequent finishing or end up in a finished garment, which must be rejected. Since the cost of a defect increases substantially as more value is put into the fabric, the lowest cost place to find a defect is just after it has been made by the knitting machine. Unfortunately, inspectors are not infallible and, in addition, are only able to reliably inspect fabric moving less than about 80 yards per minute.
Various vision inspection systems have been attempted over the years but such systems have only been able to augment the operator and have not been able to inspect fabric without the intervention of the operator. Since the operator is tied to the inspection system, he is not able to operate more than one inspection station at the same time. If the inspection station did not require the operator""s attention full time, the operator could move from one machine to another and make repairs to the fabric web as needed when the inspection system identified a defect and stopped the line.
Thus, there remains a need for an apparatus for inspecting a tubular knitted fabric wed at high speed without operator intervention while, at the same time, allows an operator to make repairs and re-start inspection easily.
The present invention is directed to a moving fabric web vision inspection system. The apparatus includes at least two electronic cameras on one side of the moving fabric web for measuring the light intensity of a predetermined area of the moving fabric web. A high frequency, backlight contrast panel on the other side of the moving fabric web provides reference point for the cameras to detect a defect. A controller connected to each of the electronic cameras generates a stop signal if the light intensity of the predetermined area of the moving fabric web deviates from a predetermined value. The predetermined value corresponds to a detected defect in the moving fabric web. Finally, a repair station downstream from the cameras allows an operator to repair a defect detected by the vision inspection system.
In the preferred embodiment, the cameras are directed at the fabric web at substantially the same field of vision xe2x80x9cwindowxe2x80x9d to improve detection reliability. In addition, the cameras are directed at the fabric web at between 20 and 0 degrees from normal to reduce the effect of xe2x80x9chourglassingxe2x80x9d of the high-speed web.
The backlight panel includes at least one fluorescent tube and high frequency ballast connected to the fluorescent tube. In the preferred embodiment, the high frequency ballast connected to the fluorescent tube is operable at about 20 kHz. to reduce flicker error. The backlight panel also may include a translucent diffuser panel between the light panel and the moving fabric web.
The repair station includes an overhead frame, a tension roll, and a doff roll downstream from the tension roll. The tension roll includes a high friction surface for engaging the fabric web. The doff roll includes a low friction surface for allowing some slippage of the fabric web. Also, the doff roll includes an anti-backlash roll positioned between 45 and 90 degrees with respect to the downstream surface of the doff roll to control the discharge angle of the fabric web.
Accordingly, one aspect of the present invention is to provide a moving fabric web vision inspection system. The apparatus includes: at least two electronic cameras on one side of the moving fabric web for measuring the light intensity of a predetermined area of the moving fabric web; a contrast panel on the other side of the moving fabric web; and a controller connected to each of the electronic cameras for generating a stop signal if the light intensity of the predetermined area of the moving fabric web deviates from a predetermined value, the predetermined value corresponding to a detected defect in the moving fabric web.
Another aspect of the present invention is to provide a moving fabric web vision inspection system. The apparatus includes: at least two electronic cameras on one side of the moving fabric web for measuring the light intensity of a predetermined area of the moving fabric web; a high frequency, backlight contrast panel on the other side of the moving fabric web; and a controller connected to each of the electronic cameras for generating a stop signal if the light intensity of the predetermined area of the moving fabric web exceeds a predetermined value, the predetermined value corresponding to a detected defect in the moving fabric web.
Still another aspect of the present invention is to provide a moving fabric web vision inspection system. The apparatus includes: at least two electronic cameras on one side of the moving fabric web for measuring the light intensity of a predetermined area of the moving fabric web; a high frequency, backlight contrast panel on the other side of the moving fabric web; a controller connected to each of the electronic cameras for generating a stop signal if the light intensity of the predetermined area of the moving fabric web deviates from a predetermined value, the predetermined value corresponding to a detected defect in the moving fabric web; and a repair station downstream from the cameras for repairing a defect detected by the vision inspection system.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.